Cruise friendly low 12's with a 340 Dart

I have considered a crate 360 or building a junk 360 with aluminum heads. I could sell my 340 and recoup alot of the costs I'm sure. I've also been told a 904 will net me a tenth or two and a lil beter mpg but I don't know if this is true or now. At this point, I'm gonna try the headers, converter, a dyno tune, and some new tires as my BFGs are worn out. I guess slicks for the track is another option.